1. Field of the Invention
The invention relates generally to scanning apparatus technology and, more particularly, to a method of scanning both sides of a document sheet by means of a scanning module.
2. Description of the Related Art
Current scanning apparatuses increasingly become more popular as their commercial prices are substantially reduced and their performances enhanced. More particularly, a current scanning apparatus is capable of scanning larger document sheets with a higher image resolution by means of an IEEE 1394 transmission interface. Conventionally, a scanning apparatus can be distinguished among different types such as a handheld scanning apparatus, a sheet feed scanning apparatus, a flatbed scanning apparatus, an overhead scanning apparatus, and a positive/negative scanning apparatus.
A sheet feed scanning apparatus may be assembled with an automatic document feeder (ADF) that includes an inlet slot through which the document sheet is inserted. Through an assembly of rollers and wheels, the document sheet then is fed in the scanning apparatus to be scanned. To further enhance the performance of the scanning apparatus, a flipping device may be additionally mounted in the automatic document feeder to turn the document sheet for capturing the images of both front and reverse sides of the document sheet. The ADF is usually placed on the scanning platform or in the upper cover of the flatbed scanning apparatus.
The design of a conventional ADF is generally complex, and the document sheet fed in the inlet slot may be subjected to jam problems. Moreover, when the scanning apparatus performs fast scanning, the resulting rapid movement of the document sheet may cause its inaccurate alignment, and an error between the image captured by the scanning apparatus and the actual image of the document sheet may occur. In addition, the ADF is usually suitable with only paper document sheets, and is inoperative for thicker documents such as photos or cards.
Instead of designing an ADF that allows flipping the document sheet to scan both front and reverse sides with one single scan head, two scan heads may be mounted to respectively capture the images of the front and reverse sides of the document sheet. However, this solution is not satisfactory because the mount of two scan heads increases the production cost, and the coordination between the two scan heads further may be complex to achieve.